"It’s a huge selling point" for prospective renters, said Jennifer Farmer. a senior property manager for the building on Seattle’s First Hill. "There’s always a ‘wow’ when we come up here."

But Seattle city leaders want to move past the "wow" factor for green roofs, and expand their use citywide. On Thursday they’re releasing areport that inventoried Seattle’s 62 vegetated roofs, which cover the equivalent of nine football fields.

"That’s a pretty big chunk of land," said Seattle City Councilman Mike O’Brien. "(But) when you think about what’s possible in a city like Seattle, that’s just a drop in the bucket."

The city’s 8 acres of green roofs and rooftop gardens account for less than 1/10 of 1 percent of roofs overall. The new report, which was a collaboration between Seattle and the University of Washington Green Futures Lab. explores the potential for and hurdles to increasing the number of planted roofs.

Green roofs, or ecoroofs, come in different forms. Some are shallow — with 3 to 6 inches of dirt — and extensive, capping most of a building with grasses and drought-tolerant sedums and plants. Others are gardenlike, with multiple deep containers suitable for veggies or larger shrubs and trees.

The roofs are most often promoted as a good way to control the polluted stormwater runoff that fouls local streams, lakes and Puget Sound. The soil and plants capture the water, allowing some of it to evaporate, get sucked up by the plants or slowly drain into the stormwater system. The most successful ecoroofs can capture more than 90 percent of a downpour.

Other benefits include protecting roofs from damage from the sun, potentially doubling the life of a roof. They can also insulate a building, cutting cooling and possibly heating costs. They offer a respite from the concrete jungle, providing welcome green spaces for bugs, birds and people. Green roofs create new real estate for increasingly popular urban farming.

"When we start to accumulate all the benefits," O’Brien said, "we’re seeing that this is a smart way to go."

Green roofs catching on

While Seattle nurtures its blossoming love of verdant rooftops, they’re already commonplace in parts of Germany and Switzerland and have been embraced in Chicago and New York.

Officials in Portland, Ore. are so sold on the green-building strategy that the city is paying building owners to install the roofs, reimbursing them for installation costs of up to $5 a square foot. Portland has set of goal of 43 acres of planted rooftops by 2013. It has nearly 12 acres of ecoroofs so far, plus an additional 15 acres of less intensively planted rooftop gardens.

When it comes to green roofs, "in Portland it seems more accepted than Seattle," said Amy Chomowicz. ecoroof program administrator for the city of Portland. "There has been tremendous interest. Frankly, it’s surprised me."

Portland’s financial support for green roofs is motivated in large part by the stormwater benefits. The city is struggling to reduce the runoff that floods the sewers during storms, sending raw sewage into rivers, harbors and estuaries. More conventional sewer fixes — building bigger pipes and treatment plants — can cost more than the ecoroofs.

Worries, however, still remain for many building owners.

"People want to know: Will the roof leak, and will it make the building collapse?" Chomowicz said. The answer to both questions is no, provided the roof is built correctly and designed to hold the extra weight, she said. After all, "any roof can leak."

Seattle’s leaders are moving a bit more cautiously than Portland’s; they’ve felt the sting of very public ecoroof snafus in recent years.

Green roofs blanketing the King County International Airport. the Seattle Justice Center and Seattle City Hall have struggled to take hold, plagued to different degrees by weeds, a lack of summer irrigation, and the need for repeated replanting.

But ecoroof supporters say the understanding of which soils and plants work best in the Northwest is quickly evolving.

"There were hiccups initially," said Sarah Reich. a policy analyst with ECONorthwest, an economic consulting firm. "The technology has really matured a lot."

One of the big lessons learned is that you can’t plant the roof and walk away. Just as homeowners have to clean the gutters and sweep moss from conventional roofs, ecoroofs require periodic maintenance, particularly when they’re new and plants are getting established.

Costs a concern

The higher upfront cost of ecoroof construction still scares some building owners away. While the roofs last much longer, a 2008 Portland study for a hypothetical large project estimated it would cost about $10 per square foot for a conventional roof, while a green roof would be nearly $16.

That gap is shrinking, however.

"The costs will go down over time," Reich said. Already she’s seen a price drop in the past 5 years. And in Oregon the number of businesses building the roofs and selling the ecoroof materials has increased, she said.

Seattle officials like the idea of growing the green roof industry up here as well, and leaders have taken steps to encourage ecoroof construction.

In 2009, changes to Seattle’s building code made it easier for developers to get credit for the stormwater benefits that come from green roofs. Taking the stormwater out of the city’s drainage system helps saves the city money by reducing flooding and maintenance costs.

Ecoroofs also count toward landscaping requirements for new projects under the Seattle Green Factor program, which was approved in 2006.

The plan now is to keep collecting data on the roofs and sharing information with other cities to develop a better understanding of the costs and benefits, and to figure out how best to keep greening the Emerald City from top to bottom.

"We’ve taken the first couple of steps," O’Brien said, "Now we need to take it to the next level."

"It’s a huge selling point" for prospective renters, said Jennifer Farmer. a senior property manager for the building on Seattle’s First Hill. "There’s always a ‘wow’ when we come up here."

But Seattle city leaders want to move past the "wow" factor for green roofs, and expand their use citywide. On Thursday they’re releasing areport that inventoried Seattle’s 62 vegetated roofs, which cover the equivalent of nine football fields.

"That’s a pretty big chunk of land," said Seattle City Councilman Mike O’Brien. "(But) when you think about what’s possible in a city like Seattle, that’s just a drop in the bucket."

The city’s 8 acres of green roofs and rooftop gardens account for less than 1/10 of 1 percent of roofs overall. The new report, which was a collaboration between Seattle and the University of Washington Green Futures Lab. explores the potential for and hurdles to increasing the number of planted roofs.

Green roofs, or ecoroofs, come in different forms. Some are shallow — with 3 to 6 inches of dirt — and extensive, capping most of a building with grasses and drought-tolerant sedums and plants. Others are gardenlike, with multiple deep containers suitable for veggies or larger shrubs and trees.

The roofs are most often promoted as a good way to control the polluted stormwater runoff that fouls local streams, lakes and Puget Sound. The soil and plants capture the water, allowing some of it to evaporate, get sucked up by the plants or slowly drain into the stormwater system. The most successful ecoroofs can capture more than 90 percent of a downpour.

Other benefits include protecting roofs from damage from the sun, potentially doubling the life of a roof. They can also insulate a building, cutting cooling and possibly heating costs. They offer a respite from the concrete jungle, providing welcome green spaces for bugs, birds and people. Green roofs create new real estate for increasingly popular urban farming.

"When we start to accumulate all the benefits," O’Brien said, "we’re seeing that this is a smart way to go."

Green roofs catching on

While Seattle nurtures its blossoming love of verdant rooftops, they’re already commonplace in parts of Germany and Switzerland and have been embraced in Chicago and New York.

Officials in Portland, Ore. are so sold on the green-building strategy that the city is paying building owners to install the roofs, reimbursing them for installation costs of up to $5 a square foot. Portland has set of goal of 43 acres of planted rooftops by 2013. It has nearly 12 acres of ecoroofs so far, plus an additional 15 acres of less intensively planted rooftop gardens.

When it comes to green roofs, "in Portland it seems more accepted than Seattle," said Amy Chomowicz. ecoroof program administrator for the city of Portland. "There has been tremendous interest. Frankly, it’s surprised me."

Portland’s financial support for green roofs is motivated in large part by the stormwater benefits. The city is struggling to reduce the runoff that floods the sewers during storms, sending raw sewage into rivers, harbors and estuaries. More conventional sewer fixes — building bigger pipes and treatment plants — can cost more than the ecoroofs.

Worries, however, still remain for many building owners.

"People want to know: Will the roof leak, and will it make the building collapse?" Chomowicz said. The answer to both questions is no, provided the roof is built correctly and designed to hold the extra weight, she said. After all, "any roof can leak."

Seattle’s leaders are moving a bit more cautiously than Portland’s; they’ve felt the sting of very public ecoroof snafus in recent years.

Green roofs blanketing the King County International Airport. the Seattle Justice Center and Seattle City Hall have struggled to take hold, plagued to different degrees by weeds, a lack of summer irrigation, and the need for repeated replanting.

But ecoroof supporters say the understanding of which soils and plants work best in the Northwest is quickly evolving.

"There were hiccups initially," said Sarah Reich. a policy analyst with ECONorthwest, an economic consulting firm. "The technology has really matured a lot."

One of the big lessons learned is that you can’t plant the roof and walk away. Just as homeowners have to clean the gutters and sweep moss from conventional roofs, ecoroofs require periodic maintenance, particularly when they’re new and plants are getting established.

Costs a concern

The higher upfront cost of ecoroof construction still scares some building owners away. While the roofs last much longer, a 2008 Portland study for a hypothetical large project estimated it would cost about $10 per square foot for a conventional roof, while a green roof would be nearly $16.

That gap is shrinking, however.

"The costs will go down over time," Reich said. Already she’s seen a price drop in the past 5 years. And in Oregon the number of businesses building the roofs and selling the ecoroof materials has increased, she said.

Seattle officials like the idea of growing the green roof industry up here as well, and leaders have taken steps to encourage ecoroof construction.

In 2009, changes to Seattle’s building code made it easier for developers to get credit for the stormwater benefits that come from green roofs. Taking the stormwater out of the city’s drainage system helps saves the city money by reducing flooding and maintenance costs.

Ecoroofs also count toward landscaping requirements for new projects under the Seattle Green Factor program, which was approved in 2006.

The plan now is to keep collecting data on the roofs and sharing information with other cities to develop a better understanding of the costs and benefits, and to figure out how best to keep greening the Emerald City from top to bottom.

"We’ve taken the first couple of steps," O’Brien said, "Now we need to take it to the next level."